Strapless prosthetic arm

ABSTRACT

Permanent magnets or electromagnets or a combination of such magnets are provided to retain a prosthetic device on an extremity, such as an arm. The prosthesis utilizes the opposing forces, which are developed by virtue of like magnetic poles being in proximity to each other, to urge the prosthesis to remain attached to the extremity. The prosthesis is prevented from rotation by virtue of a centering force that is provided by an attachment magnet in the prosthesis being placed between two implanted magnets. A removable mounting ring is placed over the prosthesis straps to maintain them in proximity to the extremity.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 60-694,012, filed on Jun. 25, 2005.

FIELD OF THE INVENTION

The present invention relates generally to prosthetics, and, morespecifically to an attachment system used in the donning/doffing and useof a socket on a residual limb. The present invention more particularlyrelates to an attachment system that utilizes magnets for mounting tothe limb and that controls rotation of the mounted prosthesis.

BACKGROUND OF THE INVENTION

It has long been appreciated that differential air pressure or “suction”may be utilized to retain or “suspend” a prosthetic limb on an amputee'sstump. Gravitational and other forces tend to cause separation betweenthe prosthetic limb and the patient's residual extremity during use.This happens, for example, during the swing phase of gait, when aprosthetic leg is additionally subjected to centrifugal forces. Patientshave worn a variety of belts, straps, cuffs and harnesses to retainprosthetic limbs against separation from the residual limb. Such devicesare inconvenient and can cause chafing against the patient's body givingrise to sores and abrasions.

The manner in which an artificial limb is suspended or attached to theresidual limb determines the amount of control an amputee has over theprosthesis. Suction suspension typically involves the utilization of asocket liner and a “hard” stump socket. The liner, which is usuallyfabricated from silicone, fits snugly over the residual limb and isenveloped by the socket. A negative pressure between the liner-sheathedstump and the interior of the socket holds the prosthesis on the limb.The suspension method is advantageous since it gives the amputee theability to better control the prosthesis and provides for useful sensoryor proprioceptive feedback. Suction suspension also makes the prosthesisfeel lighter, compared to other forms of suspension.

A valve is employed to regulate the air pressure in the socket such thatundesirable pressure differentials do not prevent or complicate thedonning and doffing of the socket. The valve also maintains suction oncethe socket has been satisfactorily clad. During donning, the patient'sliner-sheathed stump is inserted into the socket. At some stage orstages during the insertion the socket liner will form a roughlycircumferential air-tight seal through contact with the hard socket. Asthe patient's stump is inserted further into the socket, air pressureincreases under the stump. A valve permits air to escape from the socketuntil the pressure inside the socket equalizes with the ambient pressureand, hence, allows the stump to be fully inserted inside the socket. Asa result, when the stump is completely inserted in the socket, the airpressure is equal inside and outside the socket. The valve is closedallowing no air to flow into the distal end of the stump socket. Anytendency to remove the stump from the socket creates a “suction” effectthat acts to maintain the socket on the stump. In this manner, theprosthesis is held on the patient's stump. During doffing of the stumpfrom the socket the valve is opened to equalize the ambient pressure andthe pressure inside the socket, thus dissipating the “suction” effectand allowing removal of the stump.

Though the principle of employing “suction” for “suspending” anartificial limb is clear, there are practical problems. One of these isthe difficulty in providing a reliable and permanently effective seal atthe proximal open end of the socket, this issue is important inmaintaining the reduced pressure inside the socket. In some instances itis doubtful whether the suspending suctional force can independentlysupport the weight of the lower limb prosthesis. This is problematicfrom a safety stand-point, because if the suspension fails, and there isno redundant or back-up support mechanism, the artificial limb coulddetach from the patient's stump.

U.S. Pat. No. 5,376,131 to Lenze, et al. discloses a socket with anelastic diaphragm that engages a patient's stump, and attempts toprovide an effective seal, but the local constriction due to such atight fitting diaphragm can result in impairment of circulation in theamputee's residual limb. Suspension sleeves, which are substantiallyelongated bands fabricated from a resilient material and envelop part ofthe stump and part of the outer socket, have been used to providecomplementary mechanical support and may additionally function as asealing means. Since these sleeves constrictingly grip the residual limbover a wide region they can limit limb movement or be uncomfortable.

Another approach has led to design of a socket liner which is attachableat its distal end to a socket or artificial limb. In this manner, theliner is mechanically secured and can provide additional suspension, ifneeded, or can play the role of a backup suspension means. Typically,the socket liner is equipped with a detachable attachment component, atits distal end, which mates with a locking device and hence secures theresidual limb to an artificial limb. The locking devices employ aspring-loaded clutch mechanism or a pin-lock mechanism to lock to theliner attachment component. This attachment component is either abarb-shaped structure or a frictionally-retained pin. These attachmentcomponents can lock in a number of positions which affects the overalllength of the prosthesis. Though this may be advantageous, it can makeit difficult for the patient to consistently achieve the same prostheticconfiguration when the residual limb and the artificial limb arearticulated. Further, in this mode of limb suspension, the locking meansand the valve means are autonomous entities which are separatelyinvasive and additive in weight on the distal end of the socket.

Another type of suspension device is a roll-on suction socket. Thesuction socket, which is typically fabricated from silicone, is a longtubular structure with one open end. The distal end of the suctionsocket is attachable to a prosthesis via an attachment component and alocking device employing the same principle and design described above.During donning, the suction socket is turned inside out and rolled on tothe residual stump, being careful to avoid trapping air between the skinof the limb and the suction socket. Since the suction socketcreates/destroys a partial vacuum at its distal end duringrolling-on/rolling-off of the socket the function of a valve isintrinsically incorporated into the donning/doffing technique. Thus, thesuction socket is a simple and effective device to suspend a prosthesis.But, this can be misleading because the suction socket may not besealingly gripped by the hard socket, thereby converting the suctionsocket to a “traction” socket. Thus, the prosthesis is suspended ontothe residual limb by a combination of the frictional adhesive tractionof the suction socket and the locking retention due to the lockingdevice. This skin traction causes an undesirable “tethering” effect bypulling on the skin, thereby creating multiple skin problems. The lengthof the tube can also interfere with the mobility of the residual limb,especially in the case of below-knee amputees.

Once a desired suspension device has been assimilated into theprosthesis, the prosthesis must be laterally aligned with respect to theresidual limb. A typical conventional method for alignment of aprosthesis involves the use of a multi-axis slide mechanism whichadjusts with two degrees of freedom. The alignment is reached byadjusting the relative horizontal positioning between two plates, one ofwhich is attached to the distal end of the socket and the other to thetop end of the artificial limb. Each plate has a centrally located slotand the slots are perpendicularly oriented to one another. Once theproper alignment has been ascertained a fastening means, such as anut/bolt/washer combination couples the residual limb with theartificial limb. Such an alignment mechanism can be hazardous. Duringuse of the prosthesis the interface between the socket and theartificial limb is subjected to stresses and moments that can result inrelative motion between the alignment plates, thus misaligning theprosthesis. In extreme cases, the coupling plates may become unfastened,thereby, placing the patient at risk. The conventional alignment deviceadds excess weight to the prosthesis as well as adding to the cost,since it is a complicated device which is fabricated from titanium.Also, the size of the alignment device undesirably adds to the overalllength of the prosthesis, which can be problematic when accommodatinglong stump lengths.

Despite the large number of suspension options available, none act toeliminate rotation between the hard socket and the suction liner. Adesign called a “quad socket” has been also used. The quad socket isshaped in a square manner and forcing the “cylindrical” limb into thissquare receptacle makes the prosthesis less apt to rotate on the limb.This is not comfortable for the limb. Therefore, there has been a trendtoward more naturally-shaped sockets, making rotation control even moredifficult.

There is a need for an improved attachment system for prosthetics. Also,there is a need for improving retention of the stump in the socketwithout sacrificing the patient's comfort and without compromisingexpense, weight, or simplicity of use. There also is a need forimproving rotation control, which will improve the patient's overallcomfort and agility.

SUMMARY OF THE INVENTION

The invention is a prosthesis comprising at least one attachment magnetcreating a repulsive force with an implanted magnet that retains saidprosthesis on an extremity. The attachment magnet is comprised ofsamarium cobalt or neodymium iron boron. The attachment magnet isattached to an attachment flap of said prosthesis. The attachment magnetis retained against the extremity with a mounting ring. The prosthesisis rotationally controlled on the extremity by magnetic repulsive forcesbetween an implanted non-linear anti-rotation magnet and ananti-rotation flap magnet.

The novel features of the invention are set forth with particularity inthe appended claims. The invention will be best understood from thefollowing description when read in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a perspective view of an arm extremity and implantedmagnet showing the prosthesis.

FIG. 2 illustrates a perspective view of an extremity and mounting ring.

FIG. 3 illustrates a cross-sectional view of an extremity and attachmentmagnets.

FIG. 4 presents an extremity and prosthesis with anti-rotation magnets.

FIG. 5 presents an extremity and prosthesis with an alternativeembodiment of anti-rotation magnets.

FIG. 6 presents an extremity and prosthesis with alternative implantedanti-rotation magnets.

FIG. 7 presents a perspective view of an extremity and prosthesis with acombination of attachment magnets and anti-rotation magnets.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 provides a perspective view of a preferred embodiment of an armextremity 4 with internal bone 14 and prosthesis 2. A magnet 10 isimplanted in the extremity 4 to facilitate in retaining the prosthesis 2on the extremity 4 by the magnetic repelling force generated by similarmagnetic poles being placed facing each other of implanted magnet 10 andattachment magnets 8 that are securedly fastened in an attachment flap 6of the prosthesis 2. In the illustration, the north poles of theimplanted magnet 10 and of the attachment magnet 8 are repelling eachother thereby urging the prosthesis 2 into retention on the extremity 4.Attachment flap 6 may be comprised of a rigid non-magnet rigid materialsuch as a plastic or a flexible material such as a cloth.

The embodiment presented in FIG. 1 illustrates one implanted magnet 10,although it is preferable to have a plurality of implanted magnets 10disposed at intervals around the extremity 4 to facilitate creation ofan even mounting force on the top, bottom, and sides of the prosthesis 2where it is in contact with the extremity 4. Similarly, two attachmentflaps 6 and one attachment magnet 8 in each of the attachment flaps 6 isillustrated. It is preferable that the number of attachment flaps 6 becoordinated with the number and placement of implanted magnets 10 toassure that a constant and even mounting force is generated forretention of the prosthesis 2. While the attachment magnet 8 ispresented as one magnet, it may in alternative embodiments be comprisedof a plurality of magnets.

The illustrated implanted magnet 10 or the attachment magnet 8 may bepermanent magnets, such as rare earth magnet, for example samariumcobalt (SmCo) or neodymium iron boron (NdFeB), they may beelectromagnets, or they may be a combination of permanent orelectromagnets to facilitate retention and mounting of the prosthesis 2.Samarium cobalt magnets are widely available and offer the advantages ofbeing extremely strong, producible in a variety of simple or complexshapes and sizes, and being very resistant to corrosion. In addition,the magnets may be coated or plated with a protective biocompatiblecoating.

Neodymium iron boron generally exhibits poor corrosion resistance and isusually plated or coated, for example nickel plated, epoxy coated, orparylene coated. For implant applications, where biocompatibility isrequired, nickel is generally not an acceptable selection. Epoxy is notgenerally hermetic in the living tissue implant environment and istherefore not a preferred selection. Parylene is a known biocompatiblecoating material.

Other magnetic materials candidates include AlNiCo magnet alloy that iscomprised of aluminum, nickel, cobalt, and iron. It has very goodcorrosion resistance. Ceramic magnet material (also known as ferrite orstrontium ferrite) has a fair to good resistance to corrosion. Bonded orcomposite magnet materials may be made from Alnico, ceramic, NdFeB, orSmCo powders that are combined with a variety of plastic binders as amatrix. Lastly, flexible composite magnets are a mixture of ferrite orneodymium magnet powders and synthetic or natural rubber binders.

An alternate embodiment is presented in FIG. 2 where the attachmentflaps 6 are retained in the preferred position next to and in contactwith the extremity 4 by mounting ring 12, which may be a contiguous bandof material such as plastic or it may be a flexible strap design such asa strap. The mounting ring 12 is removable to facilitate placement ofthe prosthesis on extremity 4. The mounting ring 12 prevents theattachment flaps 6 from being repelled by implanted magnet 10 and by therepelling forces generated between the plurality of attachment magnets8, which would move the flaps away from the extremity 4.

The cross-section of extremity 4 and bone 14 (FIG. 3) illustrates onepreferred positioning of the two attachment flaps 6 in hemisphericalpositions surrounding extremity 4. Two attachment magnets 8 arepresented at opposing sides of the flaps 6 and are opposed by implantedmagnet 10 thereby retaining the prosthesis 2 by magnetic repulsiveforces.

In addition to retaining prosthesis 2 on extremity 4, the prosthesis isrestrained to avoid rotation about extremity 4 when in the mountedposition. Magnets are utilized to prevent rotation (FIG. 4) by virtue ofnon-linear anti-rotation magnet 16, which is implanted in extremity 4,where anti-rotation magnet 16 is shaped to present a biased repulsiveforce, as illustrated with the north magnet poles urging the like northmagnetic pole of attachment magnet 8, that is securedly mounted inattachment flap 6, to center itself between the north poles ofanti-rotation magnet 16.

An alternate embodiment (FIG. 5) presents an implanted wavyanti-rotation magnet 20 where the anti-rotation mounting feature hasbeen described, but the magnet centering force is provided by magnet 20that presents raised north poles to center attachment magnet 8.

A further alternate anti-rotation embodiment is presented (FIG. 6) wherethe centering magnetic force is provided by a plurality of implantedanti-rotation magnets 18 that operate as discussed previously. While twoanti-rotation magnets 18 are illustrated, more than two magnets may beutilized to optimize the anti-rotation feature of the invention.

An integrated magnetic mounting retention and anti-rotation prosthesis 2is illustrated (FIG. 7) wherein attachment flap 6 retains attachmentmagnet 8 which is repelled by the like-poled implanted magnet 10. Theprosthesis 2 is prevented from rotation by the opposing magnetic forcesprovided by interaction between anti-rotation flap magnet 22 and thelike-poled implanted anti-rotation magnets 18. In a preferredembodiment, at least two attachment flaps 6 provide balancing mountingand anti-rotation forces to retain prosthesis 2 on extremity 4.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is therefore to beunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

1. A prosthesis comprising at least one attachment magnet creating arepulsive force with an implanted magnet that retains said prosthesis onan extremity.
 2. The prosthesis according to claim 1, wherein saidattachment magnet is comprised of samarium cobalt or neodymium ironboron.
 3. The prosthesis according to claim 1, wherein said attachmentmagnet is attached to an attachment flap of said prosthesis.
 4. Theprosthesis according to claim 1, wherein said attachment magnet isretained against the extremity with a mounting ring.
 5. The prosthesisaccording to claim 1, wherein said prosthesis is rotationally controlledon the extremity by magnetic repulsive forces between an implantednon-linear anti-rotation magnet and an anti-rotation flap magnet.
 6. Aprosthesis comprising: at least one attachment magnet creating arepulsive force with an implanted magnet that retains said prosthesis onan extremity; and at least one anti-rotation magnet creating a forcethat resists rotation of said prosthesis by magnetic interaction with animplanted anti-rotation magnet.
 7. The prosthesis according to claim 6,wherein said attachment magnet is comprised of samarium cobalt orneodymium iron boron.
 8. The prosthesis according to claim 6, whereinsaid attachment magnet is attached to an attachment flap of saidprosthesis.
 9. The prosthesis according to claim 6, wherein saidattachment magnet is retained against the extremity with a mountingring.
 10. A method of retaining a prosthesis comprising the steps of:selecting an implanted magnet that is comprised of rare earth; selectingan attachment magnet that is comprised of rare earth; implanting atleast one of said implanted magnets; orienting at least one of saidattachment magnets on an attachment flap of said prosthesis to opposesaid implanted magnet; and retaining said attachment flap with amounting ring.
 11. The method of claim 1 0 further comprising the stepsof: implanting an anti-rotation magnet comprising at least twoanti-rotation magnet poles; and orienting a magnet on said attachmentflap having an opposing magnetic pole between said anti-rotation magnetpoles.